1. Field of the Invention
The invention relates to a method and apparatus for detecting positions of chips on a semiconductor wafer.
2. Description of the Prior Art
The position detection of chips on a semiconductor wafer is needed in the following cases, for example: a semiconductor wafer is set in an apparatus for depicting dicing lines on a dicing area called a dicer; a semiconductor wafer is set in an apparatus called a prober for checking electric characteristics of chips; a semiconductor wafer is set in an apparatus called a bonder for connecting bonding pads to exterior circuits; a semiconductor wafer is et in an apparatus called a printer for printing a circuit pattern on a semiconductor wafer.
An example of the semiconductor wafer in question is illustrated in FIG. 1. As shown, a number of chips formed on a semiconductor wafer 1 are segmented by a dicing area (street). In the manufacturing process of the semiconductor, cutting lines, or dicing lines are depicted on the dicing area, and then the semiconductor wafer are cut in a gridiron pattern to be separated into individual chips. Then, on the marginal area of each chip are connecting terminals called bonding pads 5 for connecting to exterior and complex circuit patterns 6.
One of prior arts, which relates to a method for detecting the positions of chips on a semiconductor wafer and is believed to be closest to the present invention, is U.S. Pat. No. 3,898,617, which is also assigned to the assignee of this invention, on a chip position detecting method by pattern matching. This chip position detecting method will be briefed with reference to FIGS. 3 and 4. As shown in FIG. 3, a field of detection 7 on the semiconductor wafer 1 is inputted into a TV camera 10, through an objective lens 8 and a relay lens 9. A video signal from the TV camera 10 is processed in a position detecting circuit 11 where the chip position is detected and calculated. A lamp 15 illuminates the detection field via a semitransparent mirror 16.
The chip position detection circuit 11 will be elaborated with reference to FIG. 4. The TV camera is raster-scanned by an output of a synchronous signal generating circuit 12 to drive the camera 10 thereby to extract a video signal of the detection field 7. The position (X and Y coordinates) of scanning beam at that time is successively obtained by a coordinate generating circuit 13 on the basis of the synchronous signal delivered from the synchronous signal generating circuit 12. The video signal from the TV camera 10 are digitized in accordance with the brightness. More specifically, it is converted into a binary form by a binary digitizing circuit 17 and then is applied to a temporary memory circuit 18 comprising a shift register, for example. Two-dimensional pattern data is read out in parallel from the temporary memory circuit 18 which is a dynamic memory, by means of a two-dimensional pattern quarry circuit 20. Two-dimensional patterns in the field 7 of the TV camera 10 are successively inputted into the two-dimensional pattern quarry circuit as the scanning progresses. The data are successively compared with a dictionary pattern 23a of a configuration of a reference chip previously stored in a dictionary pattern memory circuit 19, by means of a matching circuit 21. Through this comparison, a matching quantity between them is detected. As the patterns quarried by the two-dimensional pattern quarry circuit 20 are scanned, the matching quantity extracted from the matching circuit 21 is subsequently compared with the reference one in the chip position detection circuit 22. Through the comparison, when the matching quantity maximizes, the coordinate outputted at this time from the coordinate generating circuit 13 is stored. The coordinate stored is the chip position. That is to say, the chip position is thus detected.
In a usual semiconductor manufacturing process, several hundreds kinds of semiconductor wafers must be handled having several hundreds kinds of chips with various sizes 0.4 mm.times.0.4 mm to 6 mm.times.6 mm and various reflectivities owing to the use of different materials in the circuit pattern area. Therefore, the pattern matching method needs several hundreds kinds of dictionary patterns 23.sub.2 to 23.sub.p (p is 100-1000) in accordance with several hundreds kinds of chips used. For this reason, a substantially large memory capacity is necessary for the memory 24 and therefore the switching operation thereof is extremely complicated.
In order to identify the circuit pattern or the dicing area (street) for each chip by using the pattern matching method 1 mm.times.1 mm or more of size is required for the dictionary pattern. The size of the field taken by the TV camera 10 must be three times the dictionary pattern e.g. 3 mm.times.3 mm, in order to search the best matched point while shifting the pattern caught by the TV camera 10 in X- and Y-directions for each picture element. In this case, however, the resolution is poor and therefore the possible accuracy of detection is at most .+-.10 .mu.m. This is a serious problem to be solved immediately.
As described above, the conventional pattern matching method is disadvantageous in that the memory, the calculation circuit and like are very complicated and costly with poor detection accuracy. Therefore, the pattern matching method is problematic in practical use.